Holding out hope for American chestnut trees

Wednesday

Oct 31, 2012 at 2:00 AM

Back in the late 1800s when Longfellow wrote that unforgettable first line, "Under a spreading chestnut tree, the village smithy stands ...; " (from "The Village Blacksmith") I don't think he, or anyone else, would have predicted the precipitous decline of this once-abundant American hardwood.

Sue Pike

Back in the late 1800s when Longfellow wrote that unforgettable first line, "Under a spreading chestnut tree, the village smithy stands ...; " (from "The Village Blacksmith") I don't think he, or anyone else, would have predicted the precipitous decline of this once-abundant American hardwood.

It has been estimated that, prior to the early 1900s there were more than 4 billion American chestnut trees in forests covering most of the eastern part of this country (from southern New England southwest to Alabama). One out of four trees in the Appalachian Mountains were probably chestnuts. They were giants, growing straight and branch-free for the first 50 feet, reaching heights of 150 feet with fat trunks, a whopping 10 to 14 feet in diameter.

A bark fungus (Cryphonectria parasitica) that causes a disease called chestnut blight was accidently introduced into North America from Asiatic chestnuts in the late 1800s. Chestnut blight was first noticed in American chestnuts in 1904. The fungus enters a tree through wounds in its bark. Once inside, it spreads, making sunken cankers that expand around the trunk, girdling it, cutting off nutrient transport. Without nutrient transport all tissues above the canker die.

Unlike European and Asiatic chestnut trees, American chestnuts are highly susceptible to this disease. Within 40 years of its first sighting, chestnut blight had killed the majority of chestnut trees in North America, almost 4 billion in a mere 40 years!

Within those 40 years the composition of the eastern forest was permanently changed. Twenty-five percent of the forest canopy was eliminated. The loss of American chestnuts had a negative effect upon populations of black bears, turkeys, squirrel, deer and other animals that relied on chestnuts. Seven moth species that fed exclusively on American chestnuts are now extinct.

This was a major timber tree; its demise led to billions of dollars in losses to the lumber industry. Now, roasted chestnuts in a market come from blight-resistant European and Asian chestnuts.

Interestingly, the disease does not affect the roots, and while most of the trees died, sprouts still grow from the stumps and roots of old diseased trees. These sprouts typically reach a height of only 20 feet or so before they succumb to the blight. They never reach sexual maturity, so they do not produce chestnuts. They have a brief moment in the sun before the blight kills them.

I have a number of such sprouts in the woods behind my house. They are growing in amongst the pines by a meandering stream, reminders of a time long past.

However, there is hope. A number of groups and researchers are actively engaged in promoting their recovery. Two approaches seem to be working. A hypovirulent strain of the fungus can be injected into a tree. The term "hypovirulence" refers to an infection of the blight that is less virulent, less damaging to the tree. It is as if the fungus has gotten a virus — it still infects the tree, but is weakened, so the tree is able to fight off the fungus.

Resistant trees are also being developed, either by crossing American chestnuts with resistant Asian chestnuts, or by genetically engineering trees with genes that improve resistance. Earlier this year a number of resistant chestnuts were planted in Hollis, N.H., as part of a larger effort to restore chestnut populations.

Another compelling reason to restore chestnuts is the possibility that these trees can help slow climate change. A scientific paper published back in June 2009 by D.F. Jacobs, "Forest Ecology and Management," looked at the ability of American chestnuts to store carbon. American chestnuts grow faster than other native hardwoods and so are able to sequester more carbon. Maintaining and increasing forest cover has been identified as an important factor in slowing climate change.

Have an idea for a future column? Sue Pike may be reached at spike3@maine.rr.com.

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